In H.264/MPEG-4 AVC, one picture is divided into macroblocks, the respective macroblocks are encoded by generating a prediction block using inter prediction or intra prediction. The difference between an original block and the prediction block is transformed to generate a transformed block, and the transformed block is quantized using a quantization parameter and quantization matrix. The quantization parameter is adjusted per macroblock and is encoded using a previous quantization parameter as a quantization parameter predictor.
Meanwhile, in HEVC (High Efficiency Video Coding) under construction, various sizes of coding unit are introduced to obtain two times of compression efficiency. The coding unit has a role similar to the macroblock of H.264.
But, if the quantization parameter is adjusted per coding unit, the number of quantization parameters to be encoded increases as the size of the coding unit is smaller. Therefore, adjusting quantization parameter per coding unit results in greater quantity of coding bits required to encode the quantization parameter, which degrades the coding efficiency. Also, because using various sizes of coding unit makes the correlation between the quantization parameter and the previous quantization parameter weaker than that of H.264, a new method of encoding and decoding the quantization parameter is required for various sizes of the coding unit.